Oral delivery systems may control the release of substances to the gastrointestinal tract. Some systems may be designed for controlled release applications where a substance is slowly released in the gastrointestinal tract over a period of time. These systems may not be capable of encapsulating and protecting the substance as the system passes through the stomach. Thus, these systems may not be suitable for orally delivering substances, such as viable bioactive microbial species, to the small intestine. The viability of some microbial species drops to 0% after 60 minutes in a buffer solution having a pH of 2. If the microbial species are not protected while passing through the stomach to the small intestine, some viable microbes may be destroyed in the stomach, which has a pH between 1 and 2.5 and a residence time of greater than 80 minutes. The high acidity and residence time of the stomach may render these orally deliverable substances as non-viable before reaching the small intestine.
Some systems use pH-sensitive polymers that can deliver substances immediately upon entry into the upper gastrointestinal tract, where the pH is approximately 5.8. However, these systems may result in lower viabilities for substances such as anaerobic microbes and may not be suitable for orally delivering these substances to lower downstream portions of the gastrointestinal tract such as the lower small intestine, the large intestine, or the colon.